1. Field of the Invention
The present invention relates to a viewfinder unit in a camera, and more particularly, to a viewfinder unit in a camera having a viewfinder objective optical system that contributes to formation of an object image.
2. Description of the Related Art
In the past, various proposals have been made for a viewfinder unit in a camera having a viewfinder objective optical system that contributes to formation of an object image.
An example of such a viewfinder unit proposed in, for example, Japanese Patent Application No.5-84920 includes a real-image viewfinder comprising an objective lens, a first prism for forming an intermediate image provided by the objective lens in the vicinity of an emission end plane on which a range finding range setting frame is engraved, a picture size setting frame, a second prism, and an eyepiece lens which are arranged in that order along the optical axis. An auxiliary prism is then joined with a first reflector plane of the second prism. The center of the joint plane is formed as a half mirror, and the periphery thereof is formed as a total reflection mirror. Thus, various optical indications are superimposed on an image.
The viewfinder unit described in the Japanese Patent Application No.5-84920 has the advantage of superimposing an indication on the center of a viewfinder field without causing the whole field to get dark. However, no consideration is taken into display of FIG. 1 of other extra-field indications.
Another example of the viewfinder unit in a camera disclosed in Japanese Patent Laid-Open No.4-174419 includes a viewfinder optical system comprising an objective lens, a field frame and field lens both arranged in the vicinity of a real-image plane of the objective lens, an eyepiece lens for use in observing an object image formed on the real-image plane by the objective lens, and a prism being interposed between the field frame and eyepiece lens and having a reflector plane. Herein, a transparent surface is formed as part of the reflector plane of the prism so as to be perpendicular to the axis of reflected light. An information display image is displayed by transmitting it through the transparent surface.
The viewfinder described in the Japanese Patent Laid-Open No.4-174419 is useful for extra-field display but cannot superimpose an indication on the center of a viewfinder field. Moreover, it is hard to machine a glass prism, because the prism must be shaped uniquely.